1. Field of the Invention
This invention relates to vehicle suspensions and, in particular, to a torsion attenuator for vehicle frame rails.
2. Discussion of Related Art
A conventional vehicle includes a vehicle frame having a pair of longitudinally extending frame rails that support the engine and body. The frame is supported on a plurality of ground-engaging wheels that are disposed at opposite ends of a plurality of axles. The vehicle may further contain, for example, a steer axle on which the wheels are steerable by the vehicle operator and a drive axle whose wheels are driven by the vehicle engine. Each of the axles are coupled to the vehicle frame through a suspension that dampens movements transmitted between the wheels and the vehicle frame.
One conventional vehicle suspension system includes leaf springs disposed on opposite sides of a vehicle with each leaf spring coupled to the vehicle frame at first and second ends and to an axle beam between the first and second ends. However, this suspension has several disadvantages. During braking, movement of the axle causes the leaf springs to wind up, which produces a caster change in the axle and a reduction in steering stability. Additionally, leaf springs that comprise multiple leaves may produce a harsher ride as the spring flexes.
Another conventional suspension system includes the use of air springs, instead of leaf springs. An air spring may include a reinforced rubber bag pressurized with air, the bottom of which is attached to a mount that reduces the interior volume of the bag during jounce. Such a system may further include a microprocessor-controlled system to adjust the air spring and provide a more comfortable ride.
However, the section of a frame rail where a front suspension is mounted, such as, for example, the section of a frame rail in a truck, may have a reduced flange thickness. This reduced thickness does not significantly affect the performance of traditional leaf spring suspensions. A leaf spring does not load a frame rail locally since the leaf spring has considerable span which transmits torsional loads to frame rail locations that are distant from each other. However in air spring suspensions, the compactness and tighter packaging of the suspension system may not provide the same advantage. Loads to the frame, such as one wheel or two-wheel jounce, may create torsional stress in a frame rail in an air-spring design.
The inventors herein have recognized a need for a frame rail torsion attenuator that will minimize or eliminate one or more of the above-identified deficiencies.